Prepare topping -- combine all ingredients until mixture resembles fine crumbs. Stir in nuts and reserve.
Prepare batter -- cream butter until fluffy, add sugar and lemon rind and beat well. Add eggs, one at a time, and beat well after each addition. Mix dry ingredients in a separate bowl and then add dry mixture alternately with the sour cream; blending well after each addition. Spread batter evenly over the bottom of a greased 13 x 9 x 2 inch pan. Sprinkle blueberries over batter. Sprinkle reserved topping over blueberries.
Bake at 350 degrees for 30 - 35 minutes. Serve warm.
Serves: 4. Preparation Time: 30 minutes.